Grade confusion

Hi there
I really not sure which grade my answers sits at, so it would be really appreciated it some feeback and potential grade for my answer could be given. This in 2016 Q1

An enzyme is a biological catalyst that speeds up the rate of reaction by lowering the activation energy without actually taking part in the reaction. Enzymes are made up of proteins, they contain an active site to which a specific substrate binds to. The reaction either builds up the substrate or breaks apart the substrate. Binding to the active sites occurs through two models - lock and key, where the substrate fits perfectly into the enzyme or induced fit, where the enzyme changes the shape of the active site to better fit the substrate.

All stages of DNA replication require enzymes. The first stage of DNA replication, for example, requires the enzyme helicase to unzip the DNA strand and break the hydrogen bonds exposing the base pairs. As DNA replication relies on enzymes, DNA replication will take place most efficiently if enzymes are in optimum conditions. If enzymes are not able to function properly, then DNA replication and, therefore, mitosis will not be able to take place, restricting the growth of the organism.

One factor that affects DNA replication is temp. If temp is too low then the substrate will not have enough kinetic energy for successful collisions to take place, so rate of reaction and therefore DNA replication will decrease. As temp increases a greater number of successful collisions will take place, increasing rate of DNA replication. At optimum temp max number of collision will take place so rate of DNA replication will be optimised. If temp goes too high above optimum temp then the polypeptide bonds in enzyme will become distrupted permanently, changing the 3D shape of the enzyme and active site causing it to become denatured. If active site of enzyme become denatured then substrate will no longer be able to bind to enzyme decreasing rate of reaction causing DNA replication to eventually stop.

Another factor that affects enzyme during DNA replication is pH. All enzymes operate at an optimum pH where rate of reaction is maximized, and therefore DNA replication rate is maximized. Above optimum pH active site of enzyme become denatured so the substrate can no longer bind onto the enzyme which reduces and eventually completely stops rate of reaction and therefore DNA replication.

Another factor affecting enzymes during DNA replication is the presence of inhibitors. Inhibitors that either block (competitive inhibitor) or change the shape of the active site (non-competitive inhibitor) will stop the substrate from binding to the enzyme, which will stop the reactions from taking place, slowing down then complete stopping rate of reactions.

The question:
Discuss the function of enzymes in DNA replication and the factors that affect them.
In your answer include:
• a description of the structure of an enzyme
• an explanation of how enzymes function in DNA replication
• a discussion of at least three factors that affect enzymes during DNA replication.

You have written a good response. It is likely sitting at an E7.

To attain the E8, your discussion should include possible further information such as the presence/absence of limiting factors that can affect the rate of the reaction.
(Eg while the temperature is at the optimum and there is a high conc of enzymes for the reaction to occur, the rate of enzyme activity may be limited due to the presence of substrates or other limiting factors such as nucleotides /reactants.